The present invention finds utility in the field of material working machines which perform edge finishing operations on small or large sheets or continuous extrusions of various materials. Although the present invention was designed and developed to fill a need for a machine to do edge finishing on sheets of clear plastic such as LUCITE, it should be understood at the outset that the machine hereinafter disclosed and claimed is adaptable to edge finishing of sheets or exyrusions of almost any material capable of taking these shapes and of being finished, e.g., metal, wood, synthetic or composition wood products and all manner of plastic materials.
Edge finishing of sheet material has always been a difficult operation to carry out due largely, among other things, to the inherently troublesome problems of feeding the piece of material being worked upon across, over, under, or along, as the case may be, the tool which is performing the edge finishing operation. The same observation is true with regard to continuous extrusions, but the extent of the problem is not as great with extrusions as with sheets, especially relatively large sheets. Also, it should be understood that the problems sought to be solved by the present invention are those connected with material feeding for an edge finishing operation, where the quality of appearance or texture of the finished edge is of extreme importance, as distinguished from shaping, planing, routing or other edge working operations which produce or alter a basic design, contour or shape but in which the quality of appearance or texture of the machined surface is of little or no significance. These distinctions will be more apparent as this disclosure proceeds.
Referring more specifically to the problems encountered in feeding a piece of material during an edge finishing operation, it will at once be recognized by those skilled in the art that it is absolutely essential to reduce vibration of the workpiece to an absolute minimum, since vibration of the workpiece is a very significant cause of unsatisfactory edge finishing from the standpoint of the quality of appearance or texture of the finished workpiece edge. Even a minute amount of vibration can result in the surface of the edge being finished having scratches of blemishes of sufficient magnitude to render the finished edge unacceptable. Of course, vibration in the working tool would produce equally unsatisfactory results, but the present invention is not concerned with vibration in the working tool and it is assumed that such vibration is eliminated by suitable mounting of the tool and supporting components.
It is also necessary, in an edge finishing operation, to feed the workpiece at a uniform velocity as the workpiece passes by the working tool from one end of the workpiece to the other. The reason for this is that any variation in the velocity of movement of the workpiece during the finishing operation can, and very often will, result in a scratch or blemish at a specific location along the edge, or in an altogether different finished appearance or texture between different portions of the edge depending on where and for what duration a change in the velocity of the workpiece occurred. In either of these events, the quality of the finished edge would be unacceptable.
Still further, it is necessary to maintain a uniform amount of contact pressure between the edge of the workpiece being finished and the working tool in order to avoid marring the surface at different locations or imparting to the surface a slight but noticeably different texture or appearance depending upon the amount of variation of the contact pressure. Ordinarily, merely the weight of the piece of material being finished would provide the contact pressure necessary for the finishing operation; the critical factor is that while a piece of material is passing through the machine and being edge finished, the contact pressure should not vary from one end of the edge being finished to the other.
Another serious problem encountered in feeding pieces of material through an edge finishing machine is that of doing so without in any way marring, scratching, nicking, denting, or otherwise damaging any other surface or edge of the piece of material being finished. It should be remembered that ordinarily when material is being edge finished, it is otherwise in a state of completed form or fabrication and that further work will not be performed on the material prior to it being utilized for its intended purpose, either as a finished article of manufacture or as raw material for the manufacture of other articles. In either event, it may be highly desirable, if not absolutely essential, to feed the piece of material through the working machine in such a manner that other surfaces of the workpiece are not damaged.
Although the previous discussion of the most serious problems encountered in edge finishing have been considered in connection with a finishing operation which involves a rotating cutting tool of one type or another, these same problems are, for the most part, present in edge finishing operations which involve other types of working tools such as a sanding belt, an emery wheel or even a flame for edge finishing of plastic sheets by partial melting. It can readily be seen that the problems discussed above can cause at least similar if not much the same type of edge damage if they are allowed to occur during finishing operations involving rotating sanding belts for smooth finishing of wood or synthetic wood materials, emery wheels for bright finishing of metal sheets or flame for smooth polishing of thermoplastic sheets. As will be seen more fully hereinafter, the present invention is applicable to all of these types of finishing operations.
Prior art machines have offered little in the way of improvements in feeding devices for material working machines which perform edge finishing operations. Historically, material was fed by hand through such machines because no automatic feeders were available which could feed the material being finished with as much care as the machine operator, and this is true today in some types of finishing operations, particularly those involving either small parts or those involving clear plastic materials.
One rather popular type of feeding device for edge finishing machines comprises a plurality of closely spaced rollers which are synchronously driven and which are mounted on horizontal axes which are disposed at an angle to a longitudinal fence or guide which defines a path of movement for a workpiece, the rollers urging the workpiece toward the fence as it rides over the rollers. A cutting tool is mounted for rotation about a vertical axis in justaposition with the fence so that an edge of the workpiece contacts the peripheral surface of the cutting tool. There are several disadvantages to this type of feeding arrangement. One is the obvious limitation on the minimum size workpiece which can be handled by the spaced rollers and still have the workpiece move smoothly. A second is the obvious vibration which will be imparted to a workpiece passing from roller to roller, even when the workpiece spans many rollers. Another disadvantage is that the workpiece is sliding relative to the roller surfaces due to the angular mounting thereof with respect to the fance, which causes scratching and marring of smooth sheet surfaces, in some instances even through protective paper coatings applied to these surfaces. A further disadvantage is the relatively high degree of friction between the edge being finished and the fence due to the angular mounting of the rollers, which is detrimental to smooth feeding of large workpieces.
Many material working machines have clamp or vice type intermittent feeders which typically are attachments to the machine and in which the workpiece is gripped by a movable clamp and moved for a predetermined distance, after which the movable clamp releases the work and returns to its starting position while the workpiece is held by a stationary clamp. It is immediately apparent that this type of feeding device can cause considerable surface damage to finished surfaces, and does not lend itself to uniform and uninterrupted feeding of long lengths of material.
The well known ball spline feeder is also a popular feeding assembly, particularly in metal finishing machines. While it is a high-precision feeder well suited for its intended purpose, it is limited in its application to relatively small parts since the stroke of the feeding device is limited by the length of the screw.
It is also known to construct material conveying devices in which one or more pairs of opposed rollers or belts convey material from one location to another by gripping the material between the opposed rollers or belts. Such conveyors may be found in conjunction with extrusion presses, container filling machines, article handling machines, etc., where material is conveyed from one work station to another. Prior to the present invention, however, devices of this type have not been used in conjunction with material edge finishing machines.